1. Field of the Invention:
The present invention relates to biodegradable multiblock copolymers. More specifically, the invention relates to multiblock copolymers involving sequentially ordered blocks of polylactide and/or polyglycolide produced by ring-opening polymerization of lactide and/or glycolide onto either an oligomeric diol or diamine residue followed by chain extension with a difunctional compound.
2. Description of the Related Art:
Ring opening polymerization of lactones and their initiation by active hydrogen compounds to generate difunctional polymers is reported by K. J. Ivin, and T. Saegusa, Ring Opening Polymerization, Vol 1, Ch. 7 (1984), pp 461-521.
Preparation of block copolymers in which at least one block is a polylactone has been achieved either by simultaneous or sequential polymerization. For example, D. W. Grijpma, G. J. Zondervan, and A. J. Pennings, Polymer Bul., Vol 25 (1991), pp 327-333 prepared random block copolymers of e-caprolactone and lactide by simultaneous polymerization. The different reactivity ratio of the two monomers leads to a block copolymer with random block distribution. A. Hamitou, R. Jerome, and P. Teyssie, J. Polym. Sci.: Pol. Chem. Ed., Vol 15 (1977), pp 1035-1401 used bimetallic u-oxoalkoxides to prepare AB copolymers of e-caprolactone and -propiolactone by sequential monomer addition. X. D. Feng, C. X. Song, and W. Y. Chen, J. Polym. Sci.: Pol. Letters Ed., Vol 21 (1983), pp 593-600 reported the preparation of AB block copolymers of e-caprolactone and lactide using the same procedure.
Preparation of ABA copolymers through living polymerization is more difficult and requires modification of the growing AB intermediate. C. X. Song, and X. D. Feng, Macromolecules, Vol 17 (1984), pp 2764-2767 prepared ABA trtiblock copolymers of e-caprolactone-lactide-e-caprolactone by converting the PCL-PLA-OAl to PCL-PLA-(OCH.sub.2 CH.sub.2).sub.2-4 -OAl species which can reinitiate caprolactone polymerization for the third block.
Australian Published Patent Application No. 50602/90 discloses poly(ester-silicone) block copolymers wherein a hydroxyl terminated poly(organosiloxane) oligomer and a hydroxyl terminated polyester comprised of lactide and glycolide units are randomly linked by a diisocyanate compound, resulting in a random sequence of polyester blocks and poly(organosiloxane) blocks along the copolymer chain.
German Offenlegungsschrift DE391157 A1 discloses block copolymers wherein one type block is formed from an aliphatic polycarbonate, and the other type block is a polylactone, or a copolymer of a lactone and a carbonate.
Japanese Application No. 59-27923 discloses poly(ether-ester) block copolymers. These copolymers are produced in a manner similar to the Australian Published Patent application cited above by reacting hydroxy terminated polyethers and hydroxy terminated polyesters with a bis-acyl-lactone linker, to produce a random block distribution.
Barbskaya et al. in "Role of Hydroxyl-Containing Compounds in Processes of Cationic Polymerization of dl-Lactide", translation from Polymer Science U.S.S.R., Vol 25, No 1, pp. 1788-1793 (1983) describe the effect of octyl alcohol, glycolic acid and water on cationic polymerization of dl-Lactide, in the melt using SnCl.2H.sub.2 O catalyst.
In U.S. Pat. Nos. 2,878,236 and 3,169,945, lactone polyesters are described wherein the lactone starting material is identified as having at least six carbon atoms to avoid a tendency for the resulting polymer to revert to the monomer.